我希望有人可以解释加入多个表的性能与使用MINUS消除记录的性能。我查看了其他一些堆栈溢出问题，但没有看到我在寻找什么。
我认为这两个查询会产生相同的输出，我总是听到＆＃34;使用连接，使用连接！＆＃34;，特别是来自stackoverflow帖子，它们预计会更快... < / p>
这是我跑的第一个查询，我认为会慢得多，但运行起来只需要几分钟......
select some_id
from table1
MINUS
select some_id
from table2
where table2.value = 'some_value'
MINUS
select some_id
from table3
where table3.value = 'some_value'
group by some_id
这是我认为会更快的第二个查询，但现在已经运行了3个多小时（看不到结束？）
select some_id
from table1
join table2 on table1.id=table2.id
join table3 on table1.id=table3.id
where table2.value = 'some_value'
or table3.value = 'some_value'
group by some_id
我应该注意所有3个表都有＆gt; 100万条记录，每条记录高达1500万条。
修改：
抱歉 - 我打算让你知道我在这个问题中避免使用NOT EXISTS作为回应，因为我真的很好奇这两种情况。
答案 0 :(得分：0)
试试这个版本：
select some_id
from table1
where not exists (select 1 from table2 t2 on t1.id = t2.id and t2.value = 'some_value') or
not exists (select 1 from table3 t3 on t1.id = t3.id and t3.value = 'some_value')
为获得最佳效果，您需要table2(id, value)和table3(id, value)上的索引。
答案 1 :(得分：0)
首先确保你有索引，
要查看该计划，如果它正在使用全表扫描，那么继续创建索引，否则需要很长很长时间。
如果你有plsql开发人员，那么在sql窗口中粘贴查询并按F5它会给你解释计划。
或者也可以这样做，
SCOTT@research 17-APR-15> EXPLAIN PLAN FOR
2 select empno
3 from emp
4 MINUS
5 select empno
6 from empp
7 where empp.empno = '7839'
8 MINUS
9 select empno
10 from emppp
11 where emppp.empno = '7902'
12 group by empno
13 ;
Explained.
SCOTT@research 17-APR-15> SET LINESIZE 130
SCOTT@research 17-APR-15> SET PAGESIZE 0
SCOTT@research 17-APR-15> SELECT *
2 FROM TABLE(DBMS_XPLAN.DISPLAY);
Plan hash value: 4222598102
---------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 14 | 82 | 10 (90)| 00:00:01 |
| 1 | MINUS | | | | | |
| 2 | MINUS | | | | | |
| 3 | SORT UNIQUE NOSORT | | 14 | 56 | 2 (50)| 00:00:01 |
| 4 | INDEX FULL SCAN | PK_EMP | 14 | 56 | 1 (0)| 00:00:01 |
| 5 | SORT UNIQUE NOSORT | | 1 | 13 | 4 (25)| 00:00:01 |
|* 6 | TABLE ACCESS FULL | EMPP | 1 | 13 | 3 (0)| 00:00:01 |
| 7 | SORT UNIQUE NOSORT | | 1 | 13 | 4 (25)| 00:00:01 |
| 8 | SORT GROUP BY NOSORT| | 1 | 13 | 4 (25)| 00:00:01 |
|* 9 | TABLE ACCESS FULL | EMPPP | 1 | 13 | 3 (0)| 00:00:01 |
---------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
6 - filter("EMPP"."EMPNO"=7839)
9 - filter("EMPPP"."EMPNO"=7902)
Note
-----
- dynamic sampling used for this statement (level=2)
26 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 2137789089
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 8168 | 16336 | 29 (0)| 00:00:01 |
| 1 | COLLECTION ITERATOR PICKLER FETCH| DISPLAY | 8168 | 16336 | 29 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
或者如果你想使用autotrace，那么，
set autotrace on explain
这就是它的外观，
SCOTT@research 17-APR-15> select empno
2 from emp
3 MINUS
4 select empno
5 from empp
6 where empp.empno = '7839'
7 MINUS
8 select empno
9 from emppp
10 where emppp.empno = '7902'
11 group by empno
12 ;
EMPNO
----------
234
7499
7521
7566
7654
7698
7782
7788
7844
7876
7900
7934
12 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 4222598102
---------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 14 | 82 | 10 (90)| 00:00:01 |
| 1 | MINUS | | | | | |
| 2 | MINUS | | | | | |
| 3 | SORT UNIQUE NOSORT | | 14 | 56 | 2 (50)| 00:00:01 |
| 4 | INDEX FULL SCAN | PK_EMP | 14 | 56 | 1 (0)| 00:00:01 |
| 5 | SORT UNIQUE NOSORT | | 1 | 13 | 4 (25)| 00:00:01 |
|* 6 | TABLE ACCESS FULL | EMPP | 1 | 13 | 3 (0)| 00:00:01 |
| 7 | SORT UNIQUE NOSORT | | 1 | 13 | 4 (25)| 00:00:01 |
| 8 | SORT GROUP BY NOSORT| | 1 | 13 | 4 (25)| 00:00:01 |
|* 9 | TABLE ACCESS FULL | EMPPP | 1 | 13 | 3 (0)| 00:00:01 |
---------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
6 - filter("EMPP"."EMPNO"=7839)
9 - filter("EMPPP"."EMPNO"=7902)
Note
-----
- dynamic sampling used for this statement (level=2)
SCOTT@research 17-APR-15>
SCOTT@research 17-APR-15> select emp.empno
2 from emp
3 join empp on emp.empno=empp.empno
4 join emppp on emp.empno=emppp.empno
5 where empp.empno = '7839'
6 or emppp.empno = '7902'
7 group by emp.empno
8 ;
EMPNO
----------
7839
7902
Execution Plan
----------------------------------------------------------
Plan hash value: 1435156579
-------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 30 | 8 (25)| 00:00:01 |
| 1 | HASH GROUP BY | | 1 | 30 | 8 (25)| 00:00:01 |
|* 2 | HASH JOIN | | 1 | 30 | 7 (15)| 00:00:01 |
| 3 | NESTED LOOPS | | 6 | 102 | 3 (0)| 00:00:01 |
| 4 | TABLE ACCESS FULL| EMPPP | 6 | 78 | 3 (0)| 00:00:01 |
|* 5 | INDEX UNIQUE SCAN| PK_EMP | 1 | 4 | 0 (0)| 00:00:01 |
| 6 | TABLE ACCESS FULL | EMPP | 10 | 130 | 3 (0)| 00:00:01 |
-------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("EMP"."EMPNO"="EMPP"."EMPNO")
filter("EMPP"."EMPNO"=7839 OR "EMPPP"."EMPNO"=7902)
5 - access("EMP"."EMPNO"="EMPPP"."EMPNO")
Note
-----
- dynamic sampling used for this statement (level=2)